The invention is based on a fuel injection system. A fuel injection system is already known in which a portion of the fuel delivered to the fuel injection valve flows at least partially through the fuel injection valve and then back again, via a fuel discharge line, to the intake side of a fuel injection pump. In such a system, however, there is the danger that dirt particles or tiny chips, which may have resulted from the manufacturing process and could not be removed by cleaning, may get into the fuel during operation of the fuel injection system, causing the fuel injection system to malfunction. For example, such particles or chips could be deposited between the armature and core of an electromagnetically actuatable injection valve, or between the movable valve member and the fixed valve seat.